


with a name like mine

by smilebackwards



Category: Harry Potter - J. K. Rowling
Genre: Alternate Universe - Canon Divergence, Gen, M/M
Language: English
Status: Completed
Published: 2018-07-15
Updated: 2018-07-15
Packaged: 2019-06-11 00:38:22
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,370
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15303609
Author URL: https://archiveofourown.org/users/smilebackwards/pseuds/smilebackwards
Summary: Regulus spit out a mouthful of pumpkin juice when Dumbledore announced at staff breakfast that Remus Lupin would be taking over the Defense Against the Dark Arts post.Or: The AU where Regulus Black is the Hogwarts Potions Professor instead of Snape and Prisoner of Azkaban goes a little differently





	with a name like mine

**Author's Note:**

> This is based on professorsparklepants amazing [tumblr prompt](https://smilebackwards.tumblr.com/post/174352448870/professorsparklepants-chucktaylorupset): Can we have a Harry Potter AU where Regulus Black is the Death Eater spy turned potions master instead of Snape? 
> 
> '(there's no going home) with a name like mine' title is from Ghost Towns by Radical Face.

Regulus spit out a mouthful of pumpkin juice when Dumbledore announced at staff breakfast that Remus Lupin would be taking over the Defense Against the Dark Arts post.

Lupin eyed him with a tired, benign amusement. Regulus remembered him as looking perpetually tired even when they were back at school and the intervening years didn’t appear to have been kind. Although, there were rather few people they _had_ been kind to, Regulus supposed.

“Ah, Professor Black,” Dumbledore said, eyes twinkling in a way that made Regulus want to dive for cover, “if you would be so kind as to help orient Professor Lupin.”

 _Certainly,_ Regulus thought acidly, Occluding his mind. _I’d like nothing better than to spend uninterrupted time with my mad brother’s ex-boyfriend._ He pushed his chair away from the table and came to stand beside Lupin.

Lupin didn’t look amused anymore as he stared at Regulus’ face. Regulus turned away. He’d always resembled a watered down version of Sirius. The same black hair, grey eyes, and sharp features but, even after twelve years in Azkaban, there was something vivid about Sirius on his wanted posters. 

Regulus led Lupin up the moving staircases without speaking. 

Lupin skipped over the trick step automatically, seven years of muscle memory returning easily. “I remember Defense being taught on the fifth floor,” he said, breaking the silence.

“There was an over-enthusiastic use of the Blasting Curse a few years ago,” Regulus said. “The new classroom is on the third floor.”

“What do you teach?” Lupin asked.

“Potions.” Regulus hadn’t been especially gifted at it in school but he’d later been extremely motivated and spent a year studying potential ways to overcome the potion protecting Voldemort’s Horcrux. None of them had worked, and the end result had been almost being ripped to pieces by Inferi and Regulus’ exposure as a spy for the Order of the Phoenix.

It had been worth it to see the look on Voldemort’s face the split second between when he’d Apparated to the cliff face, drawn by some magical alarm, and when Regulus Disapparated away.

Regulus had survived the subsequent wizard hunt mainly by becoming a self-imposed recluse in 12 Grimmauld Place which, despite being terribly drafty and and home to a wandering lethifold, had enough dark magic protections to hold off even Voldemort’s hit squad. Spending the next two years trapped had at least given Regulus plenty of time to practice his potions. He’d gotten his mastery almost incidentally in the decade after. He could brew Polyjuice and Veritaserum by memory, but the solution to the potion in the cave still eluded him. Voldemort had probably had Snape create it. Snape had gotten his potions mastery at nineteen, the bastard.

“Ah,” Lupin said, stilted. “So you’ll be making...”

“Your Wolfsbane Potion, yes,” Regulus said, putting the pieces together. Dumbledore had told him they’d be needing monthly batches for a new professor. The werewolf revelation explained so much about Lupin. “Don’t worry, I’ve done it dozens of times.” 

“Thank you. Have you—” Lupin cleared his throat. “Is there much you can tell me about Harry? I’d like to get to know him now that I finally have the opportunity.” 

Regulus considered how to answer that. All the teachers kept a weather eye on Harry Potter. He’d defeated the most powerful dark wizard in centuries at age one, retrieved the Sorcerer’s Stone at eleven, and opened the Chamber of Secrets at twelve. Regulus wasn’t looking forward to whatever this year’s debacle would include. Somehow it was sure to involve Sirius.

Regulus felt something of an added obligation as far as keeping Harry alive since he was Harry’s goduncle, if that was a thing, and it was his brother who’d helped decimate the poor kid’s family and was reportedly out to finish the job. Though half the school was a minefield of once-removed guilt connections. Bellatrix had tortured Neville Longbottom’s parents into insanity. And Regulus himself was indirectly responsible for the death of Blaise Zabini’s father who, fourteen years ago, had been specifically detailed to kill him. Two things Voldemort never forgave were betrayal and failure.

“Harry’s very...determined. A brilliant Seeker. Bright. Maintains an E in Potions easily but it’s your class he’ll excel in. This is it by the way,” Regulus added, pushing open the classroom door.

Lupin ran a hand over the wooden desks and peered into the bookcases. “Are these the course texts?” he asked.

“Yes,” Regulus said. “Usually you’d get to choose your own but there’s only a week until term starts and we had to let Flourish and Blotts know what to order in last month so all the professors agreed on this year’s selections.” 

Lupin nodded. “I’ve read them all at least. I don’t suppose the previous professor left any notes I could make use of?”

“Well,” Regulus said, “the last two professors were that fraud Gilderoy Lockhart and a wizard being possessed by Voldemort’s incorporeal form, so even if they had, I wouldn’t recommend it. On the positive side, you can only be an improvement.” 

“Thank you for your vote of confidence,” Lupin said, deadpan.

Regulus conjured the class schedule and cast a duplication charm on it. “You’ll have the Gryffindors and Slytherins together for Harry’s year. Look out for him and Draco Malfoy; they have a rivalry. I’m sure you remember what that’s like,” Regulus said. The troubles between Sirius and James Potter and Severus Snape had been legendary. “Draco is Narcissa’s son with Lucius.” Draco had given Regulus some odd looks over the years. Regulus wondered what precisely Narcissa had told him, if anything. 

“A whole new generation,” Lupin said musingly. “Dumbledore mentioned the dementors of Azkaban might be stationed here for a time. Is that really safe for the students?”

“The Ministry doesn’t care about the safety of the students,” Regulus said, blunt. “They want Sirius recaptured and they expect him to show up here.” Regulus couldn’t believe he and Lupin had managed to go this long without saying Sirius’ name.

Lupin kept his head down, ostensibly still studying the bookcase. “Yes,” he said faintly. “Yes, I suppose he might.”

It was more likely now that ever, Regulus thought. The castle was stacked with Sirius’ closest ties: his brother, his godson, and now his lover. Sirius had never been serious about much of anything, but he’d seemed serious about Lupin.

“I’ll see you at the start of term,” Regulus said, and closed the door behind him.

-

The bottle of cheap firewhisky Regulus kept in the bottom drawer of his desk wasn’t enough recourse for dealing with Sirius breaking into Gryffindor Tower to kill his thirteen-year-old godson in revenge for the apparently beloved memory of the Dark Lord. Regulus put on his cloak and trudged down to the Hog’s Head.

Lupin was already at the bar.

Regulus considered turning around, but it was the only place within a hundred leagues that sold quality Bulgarian vodka. He pulled out the stool next to Lupin and signalled the barman for a drink. The glass that slid over to him was dirty but that was beside the point. Regulus threw the vodka down his throat and set the empty glass back on the bar with a thump. “What complete bollocks.”

Lupin hummed in mellow agreement. Regulus wondered how long he’d been here. Raising his glass, Lupin said, voice thick with sarcasm, “To Sirius Black, arsehole and escapee extraordinaire.”

“Did you ever go to see him?” Regulus asked.

“In Azkaban?” Lupin smiled bitterly. “No. Werewolves aren’t allowed visitation rights.” 

Regulus had visited Azkaban just the once. He’d downed a shot of firewhiskey, eaten half a pound of chocolate, and tipped his chin up as he walked down an ice cold corridor filled with people who’d been tasked to kill him hooting and hissing from both sides. 

Sirius was in a cell toward the end, only three down from Snape, and wasn’t that an irony to cap it all off. “Sirius,” Regulus had said, and wasn’t sure what else to say. Sirius was huddled in a corner, wearing a thin, tattered robe. There was something wild about his eyes. 

“Sirius, what happened?” Regulus tried. Details about the trial had been sketchy in the _Daily Prophet._ It had been over and done, life sentence handed down, before Regulus heard so much as a word.

“I killed them,” Sirius said, his voice chillingly blank. “James and Lily and Har— no, not Harry. Harry’s alive.”

Regulus hadn’t thought he could feel colder but hearing Sirius say the words was like being dunked in the Great Lake at midwinter. He hadn’t believed it was even possible that Sirius had truly done it, betrayed his best friend and his family to their deaths. Regulus had been prepared to throw thousands of Galleons and the political weight of an old pureblood name behind an appeal.

“Go away,” Sirius had said, eyes losing focus, and Regulus had gone.

“I wish I’d asked him why,” Regulus said to Lupin. “He told me flat out that he betrayed the Potters, but it doesn’t make sense.” All the times Sirius had told Regulus what a fool he was, only to reverse so absolutely, so irrevocably? Sirius had had access to Grimmauld Place. If he’d wanted to betray someone, why not start with his useless younger brother rather than the family of the best friend he’d adored? 

“Why did you change sides?” Lupin asked.

Regulus thought of Kreacher’s helpless weeping when he’d returned, barely alive, from what Regulus had told him would be a simple errand, an honor. “Voldemort hurt someone I cared about.” 

It sickened him now to think of all the people he _hadn’t_ cared about; the muggles and muggle-borns, half-bloods, half the world really. More. When Regulus had come to Dumbledore with the offer to turn spy, Dumbledore had looked at the Dark Mark on his forearm with both pity and contempt, and Regulus had felt far more deserving of the contempt. 

Lupin nodded sagely. “He hurt people I cared about too.” Regulus thought Lupin might be more drunk than he’d realized. His head looked ready to hit the bar.

Regulus put his gloves down where Lupin’s forehead looked most likely to impact and ordered another drink.

-

Lupin kicked Regulus’ heel under the table and Regulus snapped back to attention. Professor Sprout had evidently finished presenting her request for thirty new sets of earmuffs for the second years who’d be studying Mandrakes and the staff meeting was coming to a close.

It was difficult to go back to awkward avoidance after you’d thrown up in a gutter together so Regulus and Lupin had settled into an awkward sort of solidarity instead, sitting next to each other in staff meetings and at the head table, discussing the best ways to keep Harry alive over their dinner plates.

“I don’t suppose you know of any potions that have a mitigating effect on dementors?” Lupin asked, as the rest of the staff filed out of the room. “Harry’s having a difficult go of it.”

“Absolutely,” Regulus said. He snapped his fingers. “Tippy? Would you bring us two mugs of hot cocoa please?”

Tippy popped in, nodded, and popped away. 

When Regulus took the professorship at Hogwarts, Kreacher had insisted on drilling one of the castle house elves in everything from Regulus’ preferred breakfast foods to the way his dress robes should be pressed. Regulus wasn’t sure how Kreacher had selected Tippy, who seemed mostly bemused, but was always obliging.

Tippy returned with the cocoa, with a splash of milk and a dollop of whipped cream, just the way Regulus liked it. “Thank you.”

“Not precisely what I had in mind,” Lupin drawled, smiling thanks as he accepted the second steaming mug from Tippy who bowed and disappeared.

“I suppose the Draught of Peace might have some positive effect, but I don’t expect it’s something anyone’s ever been keen on testing,” Regulus said. “You don’t think Harry will be able to learn the Patronus Charm?”

“Oh, he’ll learn it, I have no doubt,” Lupin said, rueful. “I just don’t know how many times I can bear to watch him hit the floor trying.”

“Well,” Regulus said, “put some throw pillows down.”

Lupin rolled his eyes. “Yes, thank you, Professor Black.”

“I’ve been a teacher longer than you,” Regulus said, mock consoling. “You’ll learn these things.”

But there were things he himself never seemed to learn, Regulus thought bleakly as he and Dumbledore Apparated to a familiar black cliffside that night. The wind whipped against them while Regulus paid the blood price to open the cave. He’d cut open his palm so many times healing spells could no longer remove the scar.

Regulus had come to the cave with Kreacher dozens of times after Voldemort had been overthrown; a pilgrimage. He’d been surprised to see everything just the same as it had been after his first failed attempt on the Horcrux. The Horcrux hadn’t been moved. No further defenses were apparent. Perhaps Voldemort had assumed that since the defenses had proven successful, there was no reason to make changes. But knowing him, it was just as likely a taunt.

Luckily, Regulus found spite to be particularly motivating. 

The blood price and the boat trip across the lake of the dead were hardly significant barriers anymore. It was the potion, the Merlin bedamned potion, that was the unbreachable lock. Regulus had tried dozens of vanishing spells, heating spells, summoning spells, and forever on, all to no avail. The closest he’d gotten was tipping in a pitcher of Antidote to Common Poisons, trying to make the potion dilute and overflow. It had reached the lip of the basin and then magically drained away, back to its original state. Regulus had glared at it with bitter rage, but it had at least proven one thing: the potion couldn’t be removed, but it could be added to. The correct antidote might render it inert, harmless when drunk to retrieve the Horcrux. 

Regulus brought new potential antidotes each time for testing. All of them, save for one that had briefly turned the lurid green of the potion to an eye-searing orange, had disappeared into it as if they’d never existed. Every testing strip came back death black.

After his sixty fourth failed antidote, Regulus had snapped, the cold rage he’d been fueled by for years suddenly gone white-hot. He’d magiced up a goblet and taken the obvious bait, ignoring Kreacher’s distressed wails. He’d gotten eight goblets deep, enough to see the shadow of something at the bottom of the basin, a necklace or a locket, before he collapsed, gasping, and felt the grip of Kreacher’s dry hands on his wrists.

Regulus had woken in the Hogwarts hospital wing three days later, his body still wracked with pain, and found Dumbledore looking at him consideringly through half moon glasses. “I’m very sorry, my boy,” Dumbledore had said. “This is not a burden I should have left to you alone.”

Part of Regulus had burned with shame that he’d needed help at all, but he’d also felt an enormous swell of relief. Voldemort’s spellwork made it impossible for Dumbledore to accompany Regulus in the boat to the potion itself but it made a tremendous difference to have him waiting on the shore with _incendio_ at the ready while Regulus tested powdered bezoar, essence of Dittany, graphorn horn and billywig stings.

Regardless of the Slytherin determination Regulus possessed, it was becoming increasingly apparent that his attempts at an antidote might never bear fruit. The only other option was what Voldemort had always intended, what Dumbledore too surely understood would be necessary if time became a more urgent factor: to drink the potion dry. A sacrifice play. As Regulus had already discovered, it was impossible for a single person. He would need to order Kreacher to help him drink the final cups.

Regulus recoiled from the thought. Kreacher had helped him drink cups of milk as a child, broth when he was ill. It would be an unspeakable cruelty to force him into a grotesque parody of that kindness, to make him complicit in something that might well cause Regulus’ death. 

Perhaps next time he could try fluxweed and dragon blood, Regulus thought despondently, and climbed back into the boat.

-

On full moons, Lupin usually found Regulus before noon and apologetically requested his Wolfsbane Potion, so Regulus was surprised to find it already evening with no sign of him. It was careless, and Lupin wasn’t careless. Regulus poured the potion into a vial, stoppered it, and made his way toward the Defense classroom, fully expecting to meet Lupin in the halls.

He didn’t. The Defense classroom was empty too. A chill of foreboding ran down Regulus’ spine.

On Lupin’s desk was a large square of parchment, the ink shifting in odd patterns. Regulus stepped closer to look at it and frowned. It was a map of Hogwarts. Regulus stared at his own name on an unfurled banner in the Defense classroom. There was a cluster of overlapping student names in all the common rooms, Madame Pomfrey in the hospital wing, and—there—Remus Lupin, almost off the edge of the map, headed toward the Whomping Willow.

Regulus grabbed the map and sprinted for the grounds. At the Whomping Willow, he muttered an _imobilus_ and slipped down the hidden passageway. Like Lupin, his name disappeared off the edge of the map. The passage opened into a narrow hallway made of cheap wooden planks. Thumps and muffled voices echoed down from the second floor. Regulus climbed the creaky staircase and stopped dead. 

Lupin was there with Harry, Hermione, and Ron.

And Sirius.

It had been gut-wrenching to see the diminished version of Sirius in Azkaban and it was worse to see him now. The knobby ends of Sirius’ wrist bones jutted out beneath his thin, pale skin. Rings as dark as ink smudged beneath his eyes and his hair was wild and mussed. He looked nothing like Regulus’ brash, laughing brother who’d smoked cigarettes and ridden a motorbike and been burnt off the family tapestry.

Harry and Hermione had their wands held on Sirius, and Ron, his leg twisted unnaturally, was clutching a squirming, squealing rat to his chest. Lupin’s body language was all wrong. He was at Sirius’ side, their shoulders almost brushing, and he looked nothing so much as relieved.

“What did I miss?” Regulus asked. Before anyone could answer, he tossed the vial of Wolfsbane to Lupin. “You missed something too, by the way. Take that quick.”

Lupin’s face went bloodless and he downed the potion in one massive gulp.

“Reg?” Sirius said. He looked utterly bewildered. “What are you doing here?”

Regulus’ heart clenched tight. Sirius hadn’t called him by that nickname since they were children, before they’d chosen their colors and then decided not to keep to them. “I teach at Hogwarts.” Nice to know that Sirius hadn’t even looked him up.

“They let Death Eaters teach at Hogwarts?” Sirius asked.

Harry, Hermione, and Ron’s heads swiveled to stare at him in horror. Regulus winced. At least his aggressively tactless brother was still in there somewhere.

Surprisingly, it was Lupin who looked at Sirius with irritation and said, “They do if they were spies for the Order. You may have noticed werewolves are allowed to teach there too.”

Harry and Ron’s heads swiveled to Lupin. Hermione bit her lip.

Sirius looked flummoxed for a moment and Regulus wondered if Sirius even remembered that he’d turned coat, then Sirius shook himself and said, “Enough of this. Give me Peter. Now.” He lunged toward Ron.

Regulus stepped into Sirius’ path and shoved him backward. He wasn’t about to tell Molly Weasley, who’d sent him a chocolate cake for every birthday after he’d been revealed as a spy, that he’d let anything happen to one of her progeny. Well, anything _else._ Regulus was surprised he hadn’t gotten a Howler over the Ginny Weasley fiasco last year. Finding the words ‘Her skeleton will lie in the Chamber forever’ painted in blood on the castle wall and learning that it had referred to tiny Ginevra Weasley, Molly’s only daughter, had been a stab to the heart. Her miraculous rescue by Harry and Ron had been tainted only by the discovery of a second Horcrux in Voldemort’s old school diary. And if Voldemort had gone as far as two, who was to say there weren’t three, four, more?

 _Peter,_ Regulus thought, aware that he’d missed some sort of revelation. Sirius could only mean Peter Pettigrew, who’d been at school with them, who’d been blown to pieces by Sirius’ own wand. Regulus threw a harassed look at Lupin. 

“Sirius,” Lupin said gently. “They deserve an explanation. Harry— Harry deserves to be told the truth.”

That made Sirius pause. He looked at Harry, then quickly away, and waved a hand at Lupin who began untangling over a decade of misinterpreted history. 

Peter Pettigrew an Animagus? The Potter’s secret Secret-Keeper? A _Death Eater?_ It seemed ridiculous, and yet… Regulus remembered a meeting, only days before he’d been exposed as a spy. A new recruit, swathed in the uniform black cloak, face hidden behind the white mask, but he’d felt that he should have known them, that he’d seen their outline a hundred times. It hadn’t been Sirius; he was sure of that.

“There’s only one way to prove it,” Lupin said, taking the rat from Ron’s bitten hands. 

“Together?” Sirius said.

Lupin nodded. “Yes, I think so,” he said and together they cast a spell. 

A shudder ran through the rat and its skin seemed to bubble and swell, paws growing and turning to hands, fur disappearing to be replaced with pale skin. Finally, Peter Pettigrew crouched pitifully on the floor. 

There was a good deal of begging, to little avail. Harry offered clemency with all the ruthlessness of a Slytherin. “The dementors can have you,” he said to Pettigrew coldly.

Outside, a cloud shifted, letting a white moonbeam through the window. Lupin went suddenly rigid and let out an inhuman howl from a human throat. His body contorted, hunched and then sprawled and then spread-eagled on the floor. It looked hellaciously painful. Regulus winced at the sound of bones snapping and shifting.

Sirius’ face was panicked. “Harry,” he said. “Harry, run. Take your friends—” 

“It’s fine,” Regulus interrupted. “I’ve been brewing Wolfsbane Potion for him. He still has his mental faculties.” Lupin, now fully transformed, nodded and sat politely on his haunches, like a well-bred hunting dog. He bared his teeth at Pettigrew.

Regulus considered how they were going to make this story stick. If Sirius went up to the castle, the dementors would give him the Kiss immediately, no questions asked, no explanations heeded. Lupin was a werewolf. Ron was injured, plus he, Harry and Hermione were out of bounds past curfew. Regulus, in a twist of irony, was the only one with a shred of credibility at the moment. 

“All right,” he said, “here’s the plan. Harry and Hermione, you take Ron to the hospital wing and then tell Dumbledore he’s needed in the Great Hall. Sirius, you stay here with Lupin.” Sirius looked mutinous until Lupin nudged his muzzle against his palm. “I’ll take Pettigrew up to the castle. Pettigrew, if you try to escape, I’ll kill you. Or, if I’m not feeling merciful, I’ll let Lupin hunt you down.” 

Lupin’s mouth lolled open in a sharp-toothed grin and Pettigrew shuddered visibly. Regulus didn’t think he’d have much trouble with him.

Harry and Hermione each ducked under one of Ron’s arms and began to make their way back to the tunnel. Regulus cast a quick splinting spell on Ron’s leg as they passed him. “Thank you, Professor Black,” Hermione murmured.

 _Professor Black,_ Sirius mouthed incredulously.

In the doorway, Harry paused and twisted his neck around to look at Sirius one more time. “We’ll talk more when I’m exonerated, Harry. I promise,” Sirius said, waving him on with a weakly reassuring smile.

“If you want to stay at Grimmauld Place in the meantime, you’re welcome to,” Regulus said, awkwardly, to Sirius. “Kreacher and I cleaned it up a good deal.” There were no more doxies, and Mother had condescended to have her portrait and the Black family tapestry placed in an out of the way chamber that Regulus had tactfully framed as ‘her own private sitting room.’ Occasionally, sunlight made it in through the windows. 

Lupin snapped his jaws at Pettigrew, herding him away from the conversation, into a corner. Considerate even as a werewolf.

Sirius looked at Regulus with a cautious light in his eyes. “I’m sorry I never visited you there after you turned spy for the Order.”

“It’s all right,” Regulus said. It hadn’t been Sirius’ responsibility to come and offer Regulus absolution. Sirius had tried to prevent him from making the mistake of joining Voldemort in the first place. “I’m sorry I only came to see you in Azkaban the once.” Regulus could see now what Sirius had meant when he’d said he killed the Potters; his attempt to protect them further had backfired. The idea that he’d killed them had been more guilt than truth.

“You came to visit me in Azkaban?” Sirius said.

Regulus paused. “You don’t remember?” 

Sirius shook his head. “There isn’t much I remember from then. I feel like I was in Azkaban for maybe a month, but also like it could have been a hundred years. I don’t suppose that makes much sense.”

“No,” Regulus said, “I see what you mean.” It wasn’t quite the same, but the outside world had passed him by for years while he’d been secluded in Grimmauld Place. Time had seemed to run together.

But they had time now, to re-learn how to be a family. To add in Lupin and Harry. To invite Andromeda and Ted and Tonks for Christmas. Perhaps someday Narcissa would pen a reply to one of the letters Regulus sent every year on her birthday and Regulus could tell Draco where the path he already seemed so determined on really led. 

The future, Regulus thought, as he reached out to grip Sirius’ hand, might be so much brighter than the past.

**Author's Note:**

> I'm also smilebackwards on [tumblr](https://smilebackwards.tumblr.com/post/176001982845/professorsparklepants-chucktaylorupset) if anyone wants to talk about Regulus Black or give this a reblog!


End file.
